We visited many power supply companies during the past year, and many of them have commented, "the power supply market is dead -- there's nothing new that can be done to attract more customers." That's not entirely wrong, as PSUs are one of the components most people only think about when their old unit fails, or when building a new system. However, it's still important for power supply companies to research new technologies and features, especially if they want to stand out from the crowd. The most recent feature to make its way onto the scene is DC-to-DC technology, with several companies now sporting high-end PSUs that use it. For example, we have the previously tested Enermax Revolution 85+, Silverstone's Zeus 1200W, and Antec's Signature Series.

DC-to-DC technology is nothing revolutionary, as power supplies have always had 3.3V and 5V rails; the difference is simply that instead of taking these directly from the transformer, these rails now split off from the 12V rail -- hence, DC-to-DC. Like other companies, Seasonic has worked on implementing this technology, but they didn't want to rush the new products to market. According to Seasonic representatives, they didn't want to have end-users beta testing the technology, instead waiting until their new PSUs were truly ready for public consumption.

Today we are looking at the long anticipated M12D series, which of course features DC-to-DC technology. We want to see if there's actually difference between Seasonic's offering and the other power supplies that use this tech. Enermax already showed us that they can reach 90% efficiency with a DC-to-DC PSU, so we want to see if Seasonic can match that achievement. There's also more to building a quality power supply than raw efficiency of course, as we discussed recently, but it is worth mentioning that Seasonic has achieved 80 Plus Silver certification.

The outward appearance of the new M12D series doesn't break new ground, with Seasonic once again using their standard black design. The casing is 160 mm long, which is slightly longer than usual, but Seasonic has built PSUs for other companies that use a longer casing (i.e. PC Power & Cooling Silencer 750 Quad). Besides the DC-to-DC technology, Seasonic includes a few other interesting features, including a custom Sanyo Denki fan. The PSUs are also supposed to have very tight voltage regulation and use only Japanese manufactured capacitors. The M12D series starts at 750W and 850W, which is definitely at the high end of what most users need. We know in the past Seasonic has tended to focus on more reasonable wattages, so hopefully we will see some of the wattage models in the future.

We are testing the 850W model today, which comes with two 12V rails each rated at 40A. Again, this isn't remarkably different from other Seasonic PSUs, but it does give users plenty of juice on each rail even with sudden large peak loads. The 3.3V rail is rated at 24A and 5V rail is 30A, both of which are fine for modern systems.

Can someone explain the significance for the DC-to-DC configuration over what they or other PSU manufacturers normally do? I mean other than the odd efficiency curves, it doesn't really provide anything unique when compared to say, the Enermax. Reply

I'm guessing here and haven't checked my "facts", but I'm guessing the DC-DC conversion helps because it allows the PSU manufacturer to concentrate most of their effort on providing a clean and efficient +12V rail from the AC supply, then tag the conversion circuitry onto the end of that to generate the less critical +5V and +3.3V rails.

The alternative is to have seperate circuitry for generating +12V, +5V, and +3.3V all individually from the AC supply. Reply

It's not necessarily easier, it's just that if you first convert to 12V alone you have maximized the amount of 12V current a single transformer of a given size can produce, then let that be the primary feedback voltage to determine switching pulse width. That typically also means you can have higher ratios of 12V to 5V or 3.3V current without going out of spec. It makes more and more sense to do so when a PSU is of high wattage as it's then expected to have so much more 12V current consumption as a % of total power used. Reply

Maybe you could put a bug in Seasonic's ear about their "little" 120mm fan? Looking at the acoustic results, you can't help but wonder what a 140mm fan could have done for that curve. A 140mm might have shifted the whole curve down two or three decibels. Reply

Bear in mind half of the fan is usually covered towards the front of the PSU, I'm really not sure a 140mm fan helps at all, because that's simply more airflow that's blocked by a baffle. This baffles me (hurr)... Seems like 120mm is perfectly adequete, and more to the point, if you so wish to change the fan yourself, at least 120mm is a standard size Reply

140s are mainly interesting because they produce any given amount of airflow at a lower RPM then 120s. So rather then run it at the same RPM as the 120, and just block more airflow, they could run it at a lower RPM while producing the same airflow. Then maybe it would top out around 28DB instead of a 31DB, or idle at 15db instead of 17. Hopefully there wouldn't be a need to change the fan then. Reply